How can I make a curved ramp?
Well you could try hiding the ends of the road you want to keep the same box selecting the vertices, then by using proportional editing (hotkey "O") you can select an edge and grab and constrain it along the Z axis (the middle mouse button changes the influence).

So select and hide "H" all the parts of the road you're happy with.

So select the edge of the "peak" of where you think the curve would be.

Press "O" to turn on Proportional Editing.



Press "G" and "Z". 

While you move it up and before you confirm, use the middle mouse button to change the influence of the proportional editing tool.

Press escape if you dont want to accept and try and a different curve type (bottom tool bar next to the proportional editing icon.

Play around with it until you're happy and/or try different edges with proportional editing with a different influence to get the desired shape.